At different stages of solar panel production, there may be shadows, microcracks and other defects. This will have a influence on the conversion efficiency of turning light energy into electric energy of the battery. For the sake of enhancing the efficiency of solar cell, it is certainly worth detecting the defects of the battery. For the sake of accurately detecting the defects of solar panels, a detection method based on Dense U-Net is came up with. This method can prevent the problem of gradient from disappearing in the process of feature transfer by introducing dense connection network. The results show that this method can produce good results in defect detection.